The frame of a window or glass door is typically the most thermally conductive part of the window or door. This is especially true of aluminum frames because aluminum is an efficient thermal conductor. This presents a problem where a temperature differential is to be maintained across the window or glass door. For example, frost or condensation may form on the inside of the window frame. A known method of addressing this problem is to make an aluminum frame in which the inner and outer frame members are connected only by an insulating material and are not otherwise connected. In this way, a thermal break is introduced into the frame that significantly reduces the transmission of thermal energy from the outside surface to the inside surface of the frame.
Previously, thermally broken aluminum frames were constructed by a method sometimes referred to as "pour and cut" which involves pouring an insulating polyurethane material into a channel joining the outside and inside of the extrusion. When the polyurethane has hardened, the connecting aluminum section of the channel is cut or sawn away to create a thermal break. Such a method is illustrated in U.S. Pat. No. 3,204,324 issued Sep. 7, 1965 to Soule Steel Company and U.S. Pat. No. 4,275,526 issued Jun. 30, 1981 to Abramson. However the need to cut away part of the frame member creates a number of practical difficulties. First, the cutting procedure is time consuming and expensive. Second, the frame members must be designed so that a cutting tool can access the connecting portion of the extrusion. This second limitation is particularly important where a hollow extrusion having more than one interconnecting cross-channel is desired. In the latter case, access of the cutting tool to the area of one of the cross channels to be cut away may be obstructed by the other cross-channel. Also in some applications it may be desirable to have the outer and inner surfaces of the frame in different colours, which is not practical using the existing thermal break construction.
U.S. Pat. No. 4,323,218 issued Apr. 6, 1982 to E & E Kaye Limited discloses a method for forming thermally broken hollow extruded frames. The method involve the use of a jig comprised of an expansible tube inserted between the two frame elements. Shoe are formed on the sides of the tube which in turn act as the base of the channels for receiving the poured thermal barrier resin material. Once the material has hardened the tube is contracted and withdrawn. This method is too labour intensive and time consuming to be economical in the production of frames. Another method for forming thermally broken hollow extruded frames is disclosed in U.S. Pat. No. 4,342,144 issued Aug. 3, 1982 to Yoshida Kogyo K.K. According to a prior method disclosed in that patent, a two step method was known for making thermally broken hollow extruded frames from a single piece extrusion by first cutting a slot in the base of one of the channels and covering it with a thermally insulating strip, then introducing the thermal barrier resin into the channel and allowing it to harden. The base of the second channel is then cut, covered with the thermally insulating strip and the resin is poured into the second channel. As pointed out in that patent, this process requires two cutting steps which are time consuming, and further does not address the problem of different colours for the inside and outside of the frame. The particular method involved in that patent still utilizes a single piece extrusion, but requires only a single cutting step.
U.S. Pat. No. 4,725,324 issued Feb. 16, 1988 to Capitol Products Corp. discloses a method of making a dual thermal barrier hollow by joining separate metal shapes with a double-sided adhesive tape and then pouring thermal barrier material into two receiving channels. The difficulty with that method lies in properly aligning the two shapes when taping them together, and the only suggestion to assist in the alignment of the shapes on the tape is the use of angle brackets.
There is therefore a need for a method of making a dual thermal barrier hollow frame by joining separate frame elements rather than cutting a single element in which alignment of the two elements can be done easily and accurately.